core, eth: implement eth/65 transaction fetcher

core/tx_pool.go

@@ -864,6 +864,12 @@ func (pool *TxPool) Get(hash common.Hash) *types.Transaction {
 	return pool.all.Get(hash)
 }
 
+// Has returns an indicator whether txpool has a transaction cached with the
+// given hash.
+func (pool *TxPool) Has(hash common.Hash) bool {
+	return pool.all.Get(hash) != nil
+}
+
 // removeTx removes a single transaction from the queue, moving all subsequent
 // transactions back to the future queue.
 func (pool *TxPool) removeTx(hash common.Hash, outofbound bool) {